In language change, we usually find that words with a relatively low word frequency change at a faster rate than words with a relatively high word frequency. Reversely, in reduction processes, we observe that high-frequency words tend to change first and low-frequency words change later. How do these facts relate to variable processes in which neither analogical change nor reduction is involved? Does frequency also play a role, for instance, in stable patterns of variation or in loanword adaptation?

This dissertation investigates phonological variation and change in three case studies: the pronunciation of the long vowel <ä> in Standard German, Dutch loanword integration in Indonesian, and sequential voicing in Japanese. It shows that frequency effects occur such that relatively high-frequency words adapt to a general phonological rule and relatively low-frequency words behave differently. This exceptional behaviour of low-frequency words may be related to their relatively unstable or opaque lexical representation or their opaque morphophonological structure.

This thesis also investigates the relation between frequency effects and grammar. It is shown that these two factors are not independent, as suggested by earlier literature, but, on the contrary, intimately related. Frequency effects are sensitive to grammatical structure. This calls for an amalgamation of phonological models which were previously regarded as disconnected; therefore this thesis proposes a combined Exemplar-Prototype-Optimality theoretical model (EPOT).